In recent years, development of CDMA (Code Division Multiple Access) communication systems has proceeded apace, and the need to shift to Wideband-CDMA (W-CDMA) systems that provide a wider bandwidth than previously in order to exchange not merely voice but also large-capacity data such as images or video at high speed, and with high quality and efficiency has increased.
Communication systems adapted to these demands are generally called third generation mobile communication systems and the standards relating thereto are co-coordinated by the 3GPP (Third Generation Partnership Project), which is the world standardization organization; introduction of such systems has already begun.
In 3GPP, a DSCH (downlink shared channel) is defined as a downlink channel that is used in shared fashion by a plurality of mobiles (see 3GPP TS 25.427, TS 25.435). With DSCH, a single channel can be shared by a large number of mobiles and flexible power control can be achieved.
In this way, high-speed and high-efficiency data communication can be implemented with limited wireless resources so the importance of this technique is expected to increase in the future.
FIG. 1A to 1C show an outline of downlink data communication (communication to mobiles) in a communication system employing DSCH. This system comprises a core network 100, which is a wired network, a wireless network control device 101, base stations 102 and mobiles 103.
DSCH is the name given to the channel between the wireless network control device 101 and the base stations 102; this DSCH is mapped onto a PDSCH (physical downlink shared channel), which is one of the physical channels on wireless.
Also, for a single mobile 103, there is a single individually assigned channel, which is called a dedicated channel (DCH) between the wireless network control device 101 and a base station 102, and which is called a dedicated physical channel (DPCH) on wireless. The mapping of the channels is defined in 3GPP TS 25.301.
As shown in FIG. 1A, when data is transmitted on a DSCH, it is necessary to transmit control data, called signaling, on the DPCH. The signaling data is used to report to the mobile 103 whether or not data is present on the PDSCH, at a timing corresponding to this signaling.
Specifically, the mobile 103 is not always in receiving condition in regard to the PDSCH but only receives data on the PDSCH if signaling data has been received on the DPCH.
The ability to receive data on the DSCH therefore only exists in the case where a dedicated CH is set up in respect of the mobile 103; data cannot be received on the DSCH in the idle state or in a condition in which a dedicated channel is not set up. It should be noted that the mobile 103 is normally able to receive signaling data on the DPCH.
Mapping of the aforesaid signaling data wirelessly onto DPCH is as described above. Two methods are laid down between the wireless network control device 101 and base station 102. In one case, data is transmitted on DCH. In the other case, data is transmitted on another channel established for the signaling.
Thereupon, after the mobile 103 has received the signaling data, in order to start preparation for receiving the DSCH, the DSCH data must be transmitted later than the signaling by a delay time ΔT.
The DSCH data is transmitted in accordance with a standard timing that is set for each sector, so the reception timings thereof are the same for the mobiles 103. In contrast, the DPCH reception timings are different for each of the mobiles 103. Consequently, the aforesaid delay time ΔT also differs for each mobile 103. The wireless network control device 101 must therefore perform transmission timing control of the signaling data, in consideration the delay time ΔT for each mobile 103.
It should be noted that the delay time Δ T is respectively reported to the wireless network control device 101, base station 102 and mobile 103 by the application at the time point of call set-up.
Also, as shown in FIG. 1B, the identifier ID 104-2 that is applied to each mobile is stored in the DSCH frame 104 in addition to the user data 104-1. This is necessary in order that the DSCH frame 104 should be correctly transmitted to a specified mobile 103.
For this reason, as shown in FIG. 1C, transmission can only be effected in respect of a single mobile 103 in a single transmission slot; a DSCH frame that is transmitted in this transmission slot cannot be simultaneously received by a plurality of mobiles 103.
FIG. 2 shows an example of the processing sequence in DSCH transmission. When the wireless network control device 101 receives (step S1) user data 104-1 from the core network 100, it generates a DSCH frame 104 (processing step P1) from the information that was already set as the user data 104-1. After this, the transmission timing of the DSCH frame 104 is determined (processing step P2).
Then, after the signaling data has been generated (processing step P3), the transmission timing of the signaling data is determined (processing step P4) using the aforesaid delay time ΔT, from the DSCH frame transmission timing. The signaling data is transmitted (step S2) to the mobile 103 through the base station 102 in accordance with the signaling transmission timing.
When a mobile 103 receives signaling data, it becomes aware of the existence of a DSCH frame that is to be received on the PDSCH, and starts preparation to receive this DSCH frame (processing step P5). After this, the wireless network control device 101 transmits the DSCH frame to the mobile 103 (step S3) through the base station 102 in accordance with the DSCH frame transmission timing.
After receiving this DSCH frame, the mobile 103 compares the mobile identifier ID 104-2 in the data with its own ID (processing step P6) and, if they agree, performs subsequent data processing. Also, if the mobile ID 104-2 in the DSCH frame data does not agree with its own ID, it discards this DSCH frame (processing step P7).